This invention relates to power cylinders operated by fluid pressure and more particularly to a fluid pressure operated power cylinder including means to securely lock the piston rod of the cylinder in a desired position.
Power cylinders, either pneumatically actuated or hydraulically actuated, find many applications in modern industry. For example, power cylinders are utilized to advance the slide of a tool head in a machine tool so as to bring the cutting tool to a position to operate on a workpiece. If the piston is not locked in its position of adjustment, the associated tool may bounce back and forth or chatter when it is moved against and into the work. As a further example, power cylinders are also conventionally used to operate work holding clamps. It is essential in these situations that the cylinder hold the workpiece securely and that it maintain a holding force on the work sometimes for long periods of time. As a further example, power cylinders are used in association with the die of an injection molding apparatus to alternately open and close the die during its operating cycle. It is important in these and other applications that the power cylinder include means to ensure that the piston, and thereby the associated tool or clamp, maintains its position of adjustment irrespective of forces exerted against the associated tool or clamp and irrespective of pressure losses in the cylinder.
Various devices have been proposed to allow the piston rod to be locked in a desired position. However, all of the prior art devices suffer from the disadvantages that they are either unduly complicated and expensive and/or do not effectively maintain the piston rod in its locked disposition.